Generally, pipes used for transporting a fluid such as water, an oil, or a gas over a long distance have limited lengths, and thus flanges are formed at connecting portions to continuously connect the pipes and the flanges are connected to each other using connecting members. In addition, various methods such as a method in which connecting portions are welded, an expansion molding method, and a compression method are applied. When pipes are connected by welding, a specialized welder is needed and thermal deformation may occur during the work. In addition, in the case of an expansion molding method in which a packing is inserted between two bodies of pipes which are connected to each other, a nut is tightened to compress the packing, and a bolt is inserted into a plumbing pipe to prevent the pipes from being separated, there is a problem in that pipe deformation occurs and thus sediment is deposited in the pipe. In addition, in the case of a compression method in which a pipe is inserted into a connecting member and a packing is pressurized together with a stainless steel ring using a separate compressing tool, there is a problem in that pipe deformation occurs.
Although a pipe connecting structure including both pipes in which a plurality of recessed portions are formed at positions at which corresponding pipes are connected in a circumferential direction, a joint ring in which a plurality of protruding portions inserted into the recessed portions of both of the pipes are formed to connect both of the pipes and a packing member inserted into the joint ring to seal between the both pipes is disclosed in Korean Patent Publication No. 10-0626291, the pipes are deformed, and it is difficult to constantly maintain a fluid flow flowing through the pipes due to the recessed portions. In addition, when sediment is deposited in the recessed portions and the pipe is left alone for a long time, there is a problem in that a blocking phenomenon may occur.